Modern medical devices, including medical pumps, are increasingly being controlled by microprocessor based systems to deliver fluids, solutions, medications, and drugs to patients. Different types of medical pump systems are used depending on factors such as the dosage of fluid to be delivered, the rate of fluid delivery, the duration, and the volume of a fluid to be infused into a patient.
One example of a medical pump system used to gradually deliver small amounts of fluid to patients is a syringe pump. A typical syringe pump system includes a syringe with a plunger mounted to a housing, a motor, a pump mechanism, a pump mechanism controller, a user interface, and an alarm. The pump mechanism exerts force on the syringe plunger, and forces fluid out of the syringe into fluid lines leading to the patient. The pump mechanism includes anti-free flow claws, and a force-detecting sensor, such as a loadcell sensor.
One concern associated with using syringe pump systems is that an occlusion may occur in any of the fluid lines attached to the pump. An occlusion will cause under-delivery of the fluid to the patient, and, at the same time, pressure will build up inside the syringe and fluid lines. The built-up pressure will cause a significant bolus of fluid to be expelled through the line after the occlusion is relieved. Therefore, it is essential that the syringe pump include an occlusion detecting mechanism. One example of an occlusion detecting mechanism may be a syringe pump mechanism controller including a sensor that detects force inside the fluid lines, means for monitoring the sensor readings, and an alarm that signals to the user when a certain threshold force or pressure level has been exceeded.
One method of occlusion detection is to calculate the force on the sensor due to fluid pressure: Fpressure. In a typical syringe pump system, as shown in FIGS. 1 and 2, the following relationships are established:Floadcell=Fclaws+Fstiction+FpressureFpressure=Floadcell−Fclaws−Fstiction 
Where Floadcell is the total force sensed by the loadcell. Fclaws is the portion of the total force caused by the anti-free flow claws, and Fstiction is the portion of the total force caused by stiction. The pressure of the fluid flow in the line, Pliquid, is calculated according to the formula
            ⇒              P        liquid              =                  F        pressure                    A        syringe                        where      ⁢                          ⁢              A                  syringe          ⁢                                                      =          π      ×                        (                                    ID              syringe                        2                    )                2            
Where Asyringe is the area of the syringe and IDsyringe is the internal diameter of the syringe.
However, there are variations in stiction caused by the rubber tip of the plunger, and varying tolerances in the force caused by the anti-free flow claws. Therefore, Fpressure typically cannot be used as the single parameter to trigger the pressure alarm because there would be too many false alarms. Accordingly, there is a need for a method of monitoring Fpressure that also allows for variations in stiction and spring force in the anti-free flow claws to avoid triggering false alarms.